1. Field of the Invention
The present invention relates to a current sensing apparatus and a voltage converter apparatus, and more particularly, to a current sensing apparatus and a voltage converter apparatus which can simultaneously measure conduction currents of an up-bridge circuit and a down-bridge circuit.
2. Description of the Prior Art
Electronic devices usually have different composing elements that operate with different operational voltages. Thus, it is necessary to utilize different DC-DC voltage converters in order to achieve different voltage modulations, such as modulation for raising voltage values or degradation voltage values, and to maintain them at predetermined voltage values. Many types of DC-DC voltage converters have been widely developed and are derived from the buck/step down converter or the boost/step up converter. The buck converter can decrease an input DC voltage to a default voltage level, and the boost converter can increase the input DC voltage to another default voltage level. With development, both the buck and boost converters are varied and modified to conform to different system architectures and requirements.
Please refer to FIG. 1, which illustrates a conventional schematic diagram of a voltage converter 10. As shown in FIG. 1, the voltage converter 10 is utilized to transform an input voltage Vin into an output voltage Vout, and includes a controller 100, a gate driver 101, a driver circuit 102, an output circuit 104, a feedback circuit 106, a current sensing module 108, an error amplifier A_ERR and a pulse width modulation comparator A_PWM. The controller 100 is coupled to the gate driver 101. The gate driver 101 includes an inverter Inv1, buffer amplifiers BA1, BA2, and is coupled to the driver circuit 102 and the current sensing circuit 108. The driver circuit 102 includes switch transistors SW1, SW2, and is coupled to the output circuit 104 and the current sensing circuit 108. The output circuit 104 includes an inductor L1 and a capacitor C1, and is coupled to the feedback circuit 106. The feedback circuit 106 includes resistors R1, R2 and is coupled to the error amplifier A_ERR. The pulse width modulation comparator A_PWM is coupled to the current sensing circuit 108 and the controller 100. The current sensing circuit 108 includes a current comparator A_CS, a current generator Cs, a capacitor C2, an inverter Inv2 and switch elements S1, S2.
In simple, the controller 100 utilizes a pulse width modulation signal or a reset signal Rst to generate a control signal to be transmitted to the gate driver 101. The gate driver 101 utilizes the control signal to correspondingly switch on/off the switch transistors SW1, SW2. Accordingly, the input voltage Vin is transformed into the output voltage Vout via the switch transistors SW1, SW2 and the output circuit 104. The feedback circuit 106 utilizes the resistors R1, R2 to transform the output voltage Vout into a feedback signal to be transmitted to the error amplifier A_ERR. The error amplifier A_ERR compares the feedback signal and a reference voltage Vref to output an error signal. The current sensing circuit 108 utilizes the current comparator A_CS to compare conduction currents passing through two points P1 and P2 of the switch transistor SW2, so as to generate a comparison signal. The current generator Cs utilizes a resistor (not shown in the figure) to transform a difference between the input voltage Vin and the output voltage Vout into a current source to be outputted. Lastly, the control signal is utilized to switch on/off the switch elements S1, S2 such that the comparison signal or the current source is utilized to charge the capacitor C2 to generate a charging voltage value. The pulse width modulation comparator A_PWM compares a difference between the charging voltage value and the error signal to generate the pulse width modulation signal to be transmitted to the controller 100. In other words, the voltage converter apparatus 10 simultaneously utilizes the reset signal Rst and the pulse width modulation signal to correspondingly change a duty cycle for driving the driver circuit 102, so as to adaptively transform the input voltage Vin into the output voltage Vout to satisfy different users' requirements.
However, inductance changes of the inductor L1 may correspondingly change an inductor-current slope between an input stage and an output stage, so as to change values of the output voltage as well as the feedback signal. In the voltage converter apparatus 10, a circuit designer must predetermine values of the input voltage Vin and the output voltage Vout, so as to pre-store the above values inside the current comparator A_CS as the charging voltage value of the capacitor C2. Therefore, users are unable to utilize the current sensing circuit 108 to immediately respond to related conduction information of the voltage converter apparatus 10, which may influence generation of the pulse width modulation signal to reduce efficiency or accuracy for transforming the input voltage Vin into the output voltage Vout.
Besides, conduction periods of the switch transistor SW1 and SW2, i.e. the value of the duty cycle generated by the gate driver 101, may influence the generation of the pulse width modulation signal. For example, a ratio of turning on the switch transistors SW1 and SW2 is 9:1, respectively. Since the conduction period of the switch transistor SW2 is too short or a switch frequency of the switch transistor SW2 is too high for the users to measure the conduction current passing through the switch transistor SW2. The users may have difficulties obtaining the related conduction information of the switch transistor SW2, such as a slope change of the conduction current passing through the switch transistor SW2. Accordingly, the product application of the voltage converter apparatus 10 will be limited.
Therefore, it has become an important issue to provide an adaptive current measurement module for the voltage converter apparatus to improve efficiency/accuracy of transforming the input voltage into the output voltage.